The present invention claims priorities of Japanese Patent Applications Serial Nos. H10-248793 and H10-272000, the contents of which is incorporated hereinto by reference in its entirety.
1. Field of the Invention
This invention relates to an image taking apparatus such as a digital camera.
2. Description of the Related Art
As a silver-halide camera, a single-lense reflex camera equipped with an interchangeable photographing lens is known. As shown in FIGS. 8 and 9, the silver-halide single-lense reflex camera is comprised of a box-shape camera main body 202 and a photographing lens 204 interchangeably attached to a front surface of the camera main body 202 via a mounting portion 203.
In the camera main body 202, a film 206 is installed at a rear portion of the main camera body 202 so as to be positioned on a focal point of the lens unit 205 of the photographing lens 204. A focal plane shutter 207 is provided in close proximity to the front of the film 206. In front of the focal plane shutter 207, a quick return mirror 209 is provided. The quick return mirror is pivoted by a pivot shaft 208 to change the position between an up-position and a down-position. Also provided in the camera main body 202 is an AF (Automatic Focussing) sensor 210 for receiving an optical image of an object passed through the lens unit 205 to detect the focussing status of the optical image formed on an image focussing surface of the film 206.
Above the quick return mirror 209, a focussing screen 211 for reproducing the focussed image formed on the image focussing surface of the film 206 is provided so as to be located in a plane equivalent to the image focussing surface. Provided on the camera main body 202 is a penta-finder 212 including a penta-prism 214 for reflexing the optical image of the object focussed on the focussing screen 211 to a rear ocular 213. Furthermore, a light sensor 215 for measuring the luminance of the object is equipped in the finder 212.
In the silver-halide single-lense reflex camera, as illustrated by the actual line in FIG. 8, the quick return mirror 209 is normally positioned such that the pivotal end (i.e., upper end) of the mirror 209 is positioned near the upper portion of the film 206 and the opposite end (i.e., lower end) thereof is located near the photographing lens 204 so as to be inclined by 45 degrees to the light axis. Depressing the shutter button 216 causes the quick return mirror 209 to rotate about the pivot shaft 208 in the direction of the arrow to the horizontal position indicated by the imaginary line in FIG. 8. Then, the focal plane shutter 207 opens, which in turn causes the object image confirmed through the finder 212 to be focussed onto and recorded by the film 206.
In the meantime, with the progress of the semiconductor technology, a digital camera in which an image pick up element such as a CCD (Charged Coupled Device) is used in place of the film 206, has been spreading recently. In such a digital camera, the image pick up element photoelectrically converts an optical image of an object into electric signals, which are then subjected to image processing to generate image data. The image data is recorded in a recording medium, such as a memory card, or is reproduced on a display of a camera main body or a personal computer.
While the use of digital cameras have spread widely, it has been proposed to make the maximum use of the resources of a silver halide camera. In other words, a digital camera utilizing a camera main body 202 and a photographing lens 204 of a silver-halide single-lens reflex camera, has been proposed. In such a digital camera, an image pick up element, such as a CCD, is generally provided at a film position (lens back position) to receive an optical image of an object focussed by the photographing lens 204 when the quick return mirror 209 is upwardly moved by fully depressing the shutter button 204.
The light receiving surface of the image pick up element in such a digital camera is generally covered by a protection glass layer. In addition, the pixels constituting the image pick up element are regularly arranged. Therefore, if the image pick up element is utilized as it is, influences of return noises cannot be avoided. To prevent such noises, an optical low pass filter is generally disposed on the front surface of the image pick up element.
Since for a silver-halide single-lens reflex camera the thickness of the film 206 is several tens microns, a required depth from the image focussing surface for installing the film 206 is slightly larger than several tens microns. Accordingly, a silver-halide single-lens reflex camera is designed to have such a depth.
In a digital camera, the image pick up element and the optical low pass filter are large in thickness. Especially, the optical low pass filter is relatively thick. Therefore, it is very hard to install the optical low pass filter in a narrow limited space between the image pick up element and the quick return mirror 209.
So long as the camera main body of the silver-halide single-lens reflex camera is utilized, it is impossible to change the distance from the mounting portion 203 to the image focussing surface. Furthermore, the location of the quick return mirror 209 cannot be changed because the focussing status on the image focussing surface should be reproduced on the focussing screen 211.
Therefore, if an image pick-up unit including the image pick up element and the optical low pass filter is positioned on an appropriate portion, a mechanical interference may occur between the quick return mirror 209 and the image pick-up unit. Such a mechanical interference may cause a damage of the quick return mirror 209 or a shift of the image pick up element which in turn causes an out-of-focus.
The focal plane shutter 207 can be removed because the image pick up element itself has a function for controlling the exposure start and terminate timing (electronic shutter function). However, removing the quick return mirror 209 causes a big mechanical change, which eliminates the effective use of the resources of a silver halide single-lens reflex camera.
To avoid the mechanical interference as mentioned above, it has been proposed to utilize a thin optical low pass filter. However, thinning the filter causes a deterioration of the filtering function, which in turn deteriorates the quality of the image to be obtained.
Another proposal for solving the above mentioned problems is to dispose an optical low pass filter around the lens mounting portion 203 in front of the quick return mirror 209. However, this will arise such a problem that some photographing lenses cannot be used because rear lenses thereof comes into contact with the optical low pass filter.
Furthermore, an infrared cutting filter is sometimes mounted in front of the image pick up element to solve the luminosity difference between the image pick up element and the human""s eyes. In this case, however, the similar problems as in the optical low pass filter will also arise.
Therefore, it is an object of the present invention to provide an image taking apparatus which can prevent a mechanical interference between an image pick up unit for picking up an optical image passed through an image taking lens and a mirror which is capable of changing a position thereof between, one being on an optical path of the image taking lens and the other being off the optical path.
It is another object of the present invention to provide an image taking apparatus which can effectively prevent a damage of the mirror and an occurrence of out-of-focus, and allow a wide selection of an image taking lens.
According to one aspect of the present invention, an image taking apparatus includes an image taking lens, a mirror which is capable of a pivotal movement such that the mirror changes a position thereof between a first position where the mirror is disposed on an optical path of the image taking lens and a second position where the mirror is disposed off the optical path, an image pick-up unit for picking up an optical image focussed by the image taking lens, and a driver for moving the image pick-up unit along a direction of an optical axis of the image taking lens in accordance with the pivotal movement of the mirror.
With this image taking apparatus, the image pick-up unit moves so as to avoid a mechanical interference with the mirror. For example, the image pick-up unit advances to an image pick-up position when the mirror rotates to an image taking position when taking an image, and returns to a standby position when the mirror returns to an original position after taking an image.
It is still another object of the present invention to provide an image taking apparatus which comprises an image taking lens, a mirror for changing a direction of an optical bundle introduced from the image taking lens by pivoting the mirror about a pivot axis member and an image pick-up unit for picking up an optical image taken by the image taking lens. The mirror is provided with a space for avoiding a mechanical interference with the image pick-up unit.
It is still another object of the present invention to provide an image taking apparatus which comprises an image taking lens, a mirror for changing a direction of an optical bundle from the image taking lens by pivoting about a pivot axis member and an image pick-up unit for picking up an optical image taken by the image taking lens. The image pick-up unit is disposed so as to be shifted to an optical axis of the image taking lens.
A mechanical interference between the mirror and the image pick-up unit can be avoided by forming a space of the mirror or shifting the image pick-up unit against the optical axis of the image taking lens.